The investigation of the route of HS1 through the Thames Marshes required an innovative approach to mitigation in order to find and reach the deeply buried, but highly significant, palaeoenvironmental and geoarchaeological sequences. Field survey included geophysical investigation of buried sediment bodies, the use of boreholes, cone penetration testing and conventional test pitting and trenching.
Early on in the construction project, it was evident that a geoarchaeological approach would be necessary because of the depth of sequences and the relative invisibility of the archaeological resource, both within the Historic Environment Record, and to conventional archaeological prospection.
As Martin Bates and Liz Stafford describe in the Oxford Wessex Archaeology monograph, Thames Holocene: A Geoarchaeological Approach to the Investigation of the River Floodplain for High Speed 1, 1994-2003, the project was highly successful in predicting the location of buried archaeological remains in a number of locations. Key amongst these are extensive remains excavated in the Ebbsfleet Valley, Mesolithic flint scatters at Tank Hill Road, Aveley, and Late Upper Palaeolithic and Neolithic scatters on Swanscombe Marsh. Other sites described here include an in situ Early Neolithic flint scatter and evidence of seasonal Roman and medieval activity on Rainham and Wennington Marshes. As important, in addition to the archaeological results, this work also presents the methodological approach that was adopted for the investigation of approximately 18km of the HS1 route across an area of thick alluvium.